During the brief history of computers, system administrators and users have been plagued by attacking agents such as viruses, worms, and Trojan Horses, which are designed to disable host computer systems or propagate themselves to connected systems.
In recent years, two developments have increased the threat posed by these attacking agents. Firstly, increased dependence on computers to perform mission critical business tasks has increased the economic cost associated with system downtime. Secondly, increased interconnectivity among computers has made it possible for attacking agents to spread to a large number of systems in a matter of hours.
Many network systems employ proxy servers to provide additional protection against attacking agents. These proxy servers manage interaction such as HyperText Transport Protocol (HTTP) communications between client systems and outside systems. This manner of setup allows network administrators to control and monitor those sites which are accessed by users and institute an additional layer of protection by configuring the proxy server to scan any incoming files for infection by attacking agents.
However, this additional layer of protection can place significant performance demands on the proxy and greatly increase transmission latency. Many attacking agents can be detected only after a file has been fully downloaded. Detection of these agents typically requires access to non-sequential sections of the file as well as the ability to emulate the execution of the file and monitor its output. The time required to fully download a large file and scan it before beginning to transmit the file to a client can generate frustrating delays for users of client systems.
What is needed is a method for reducing the latency of files transmitted through scanning proxy servers.